Inverse neutral telegraph repeater concentration group switching



MW 23 3944- A. R. BoNoRDEN ET AL f 2I34958' INVERSE NEUTRAL TELEGRAPHREPEATER CONCENTRATION GROUP S'WITCHING Filed Oct. 24, 1940 6Sheets-Sheet 1 JAL/(RE CEA ARGE n/.I/.L MMAR ALL WJ j ATTORNEY 2,349,5@6INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING 6Sheets-Sheet 2 MW 23 39ML A. R. BONORDEN ET Al.

Filed oct. 24, 1940 mSvNN BONORDE/v KOOS A TTORA/EV May 23, w44 A. R.BONORDEN ET A1. 2,349,586

INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING Filedoct. 24. 1940 e sheets-sheets EAS T LINE P. V. /fOOS /NI/ENTORSIJ.A.KREC`EK W VLA/PG E TAMARS AL By A INVERSE NEUTRAL TELEGRAPH REPEATERCONCENTRATION GROUP SWITCHING 6 Sheets-Sheet 4 23, W44 A. R. BoNoRDl-:NET AL Filed oct. 24, 1940 QOL QS SE May 23, T944. A, R, BONORDEN ET AL2,349,586

INVERSE NEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING Filledoct. 24, 1940 e sheets-sneeze 5y W MA ALL g l Z C? ATTORNEY RVAVA APJWT/N VE N TORS Patented May 23, 1944 UNITED STATES PATENT OFFICE INVERSENEUTRAL TELEGRAPH REPEATER CONCENTRATION GROUP SWITCHING New YorkApplication October 24, 1940, Serial No. 362,548

21 Claims.

This invention relates to telegraph systems and more particularly totelegraph systems wherein private branch lines are associated together,in local, state-wide, or nation-wide networks on a semipermanent basisas distinguished from a telegraph exchange switching system.

An object of this invention is the improvement of arrangements forassociating telegraph circuit elements, such as lines and station loopsin telegraph networks on a semipermanent basis, in order to facilitateadditions to and subtractions from the network and to facilitatethe'substitution of new circuit elements for existing circuit elernents,as Well as the testing of the various circuit elements in telegraphnetworks.

The operation of telegraph systems wherein private telegraph lines areassociated together into networks which remain interconnected forindefinite periods has heretofore been characterized by a lack offlexibility. That is to say,` the addition to the network, or thesubtraction from the network of telegraph lines or station loops, or thesubstitution in the network of one telegraph line or station loop foranother, re-

quired compensatory adjustments of one or more of the telegraphrepeaters in the network, because the repeaters were arranged in seriesand the current in the various repeaters was affected when theresistance was changed as the network was altered. Furthermore, addedrepeaters had to be adjusted to provide the proper polarity as well astype of operation, such as half or full duplex operation.

To overcome this diiiiculty, a new type of telegraph repeater wasdevised, which provides what is known as the inverse neutral type oftransmission on the drop side, for use primarily in service whereprivate telegraph lines were associated in networks on a semipermanentbasis. The operation of such inverse neutral repeaters is described inPatents 2,056,277, F. S. Kinkead et al., October 3, 1936, 2,069,224, G.C. Cummings, February 2, 1937 and 2,069,251, F. S. Kinkead, February 2,1937.

When circuit elements of a private line network appear in a telegraphoiice in which the new inverse neutral repeater is used, as described inthe above-mentioned patents, each telegraph station loop and telegraphline is connected into what is known in the art as a concentration groupthrough its own individual inverse neutral repeater. The drop sides orlegs of all of the line repeaters and station loop repeaters areinterconnected through a common point, which is otherwise known as thehub of the concentration group. From this common point or hub, the legof each line repeater and station loop repeater extends in seriesthrough the armature and marking contact of a receiving relay andthrough the winding of a sending relay to negative battery common to allrepeaters. This common battery has its positive terminal grounded. Nocurrent flows through the various legs of a concentration group duringthe marking condition. For the spacing condition, the armature of thereceiving relay in a partcular leg is actuated to engage with a groundedcontact. This causes current to ilow through each of the other legstoward and through the hub point to ground through the single spacingcontact. A sending relay having a winding in series in each of the otherlegs is energized to transmit the spacing signal to the circuitconnected to each of the other legs in the same concentration group.

For the full duplex condition two independent hubs are provided, as itis impossible to transmit in two directions simultaneously through asingle hub. The transmission in each set of connected legs is otherwisethe same as for the half duplex condition.

It may be observed, therefore, that in the use of inverse neutralrepeaters the legs of the various repeaters, when joined in aconcentration group, are all connected in parallel. One end of each legis joined at the common electrical point or hub. The other end of eachleg terminates in battery of the same potential and magnitude formarking. Any repeater when sending toward the hub connects ground to thehub point and transmits signals simultaneously to all other legs in theconcentration group. The signals are open and close or neutral signals,as they are known in the art, but they are inverted from the usual, inthat the marking signals are rio-current signals and the spacing signalsare current signals, hence the term in- Verse neutral.

When each loop leg and each line leg is terminated in its own individualinverse neutral repeater, it becomes electrically, for the purpose ofconnection into a concentration group, an independent unit. Since eachrepeater leg of a line or loop radiating from the hub point termihatesin battery of the same polarity and magnitude for the marking condition,so that no current iows for this condition, and since, electrically,ground is connected, as a practical matter, directly to the hub pointfor the spacing condition, the current conditions in any leg when it isreceiving from the hub, are unaffected by the addition or subtraction ofanother leg to the concentration group or by the substitution of adifferent leg for any leg forming part of a concentration group. Whentransmitting toward the hub, the only eifect is a change in magnitude ofspacing current in the transmitting leg, from the single spacing contactto the hub point, as the number of connected legs is changed.

When the circuit elements of private telegraph line networks arearranged so that each includes its own inverse neutral telegraphrepeater and becomes, for the purposes of association into a network, anelectrically independent unit, it is possible to terminate the legs ofline repeaters and loop repeaters in a switchboard and to make suchchanges in private line concentration groups as may be necessary, simplyby a switching or patching operation at the switchboard, without thenecessity for making poling or current adjustments in the leg side ofthe various repeaters in the concentration group to accommodate suchchanges. As will be shown later, the type of operation, viz. half orfull duplex, of any line repeater is automatically effected at the timethe repeater is patched.

In one of its major aspects, therefore, this invention is a switchingsystem for inverse neutral telegraph repeater circuits, adapted toexploit the inherent characteristic of inverse neutral repeaters that,for the purpose of association in concentration groups, each telegraphline or loop leg. equipped with an inverse neutral repeater, iselectrically an independent unit.

In this invention, control circuits are arranged to adapt inverseneutral repeater circuits, as used in semipermanent concentrationgroups, so that they may be controlled at telegraph switchboardpositions. To this end, telegraph line circuits extending to telegraphcentral offices in distant cities are equipped with inverse neutralrepeaters and their legs are extended through leg multiple iack circuitswhich provide a jack appearance within reach of each attendant in theline-up of switchboard positions. This makes every telelgraph linefacility available, through the medium of a jack outlet, to everyswitchboard attendant in the switchboard line-up. The line side of theline repeater circuit isadjusted once for all, so as to provide theoptimum signaling conditions Since the leg of each line circuit in theboard is equipped with an inverse neutral repeater, and is, therefore,an independent entity electrically, it may be used to communicate withthe distant central oiice as a separate facility. Or it may be added toa network without the necessity for compensatory adjustments on the legside.

In this invention, an appearance of a particular private line networkmay include a number of station loops, extending from various points inthe local area where one of the switchboard lineups of this invention isassumed to be located, into the switchboard. Each of the local stationloops will have an independent inverse neutral loop repeater connectedto it. Each leg of such loop repeater will be terminated in a particularposition in the board in a group of three jacks which will be termedhereafter loop concentration jacks. All of the ,jacks associated withloop circuits which are to be formed into a pai'- ticular concentrationgroup will appear, preferably side by side, at some one position in theswitchboard line-up, so that the loop circuits may be administered by anattendant at that position. The loop jacks may be multipled to a secondposition, so that at times, a second attendant may supervise theconcentration group. The line circuits, the repeater legs of which, ashas been pointed out, are multipled throughout the board, must beinterconnected to the loop circuits so that the concentration group maybe extended to other portions of the network appearing in switchboardsin distant Cities as required. This is done by selecting the proper linefacilities from the entire group which are multipled throughout theboard and extending the leg of each one which is required into a groupof three other jacks, termed line concentration jacks, each group ofjacks being individual to a line circuit at the particular positionwhere the .concentration group is to be administered. The legs of eachof the loop and line repeaters which are to be associated in aparticular concentration group, after passing through its individualgroup of jacks at a particular attendants position, are all joined in acommon electrical point which becomes the hub of the concentrationgroup.

The connecting together of the individual leg conductors to form the hubmay be effected in any convenient manner. In order to reduce thepossibility of disconnecting any line or loop inadvertently from aconcentration group with which itis normally associated, the individualconductors may be extended to individual punchings on a terminal stripand strapped together with a common soldered connection. When thusassembled, the line circuits and loop circuits in a concentration groupeach have groups of jacks, individual to each line circuit and loopcircuit, all ofwhich appear before a particular attendant in theswitchboard line-up who is responsible for the administration of theservice. Since, as has been pointed out above, all of the telegraphlines from distant cities, which come into the telegraph office wherethe switchboard of this invention is assumed to be located, are eachequipped with an individual inverse neutral repeater which makes it anindependent entity and each line has an appearance, in the form of amultiple jack, within cord reach of each attendant, any idle line in themultiple'may be connected on a temporary basis into a particulartelegraph network by a patch from the multiple at the position into oneof the concentration jacks at the particular position where theconcentration group for that network appears. It is to be understood, ofcourse, that the bank of line leg multiple jacks extending through theswitchboard are terminations of circuits which extend to many diiferentcities and it is necessary to select one extending vto the properdestination. This may be determined from reference to the jackdesignation strip.

The normal network, as required to provide the proper number oftelegraph lines to distant cities and the proper number of loops tostations in the local area served by the switchboard of this invention,will be set up in what is essentially a permanent concentration group.Each line and loop leg will be extended through its own individual groupof concentration jacks in the switchboard position where theconcentration group is to be administered and joined together in a hub,preferably by a soldered connection. The jacks in the various individualline and loop legs provide means for making changes in the network yasrequired on a temporary basis by means of patches. They also providemeans for testing, monitoring, measuring bias, communicating with theattendant. etc., and, in general, permit the complete administration ofthe various private line networks, the testing and supervision of theelements of a network, the addition of lines or loops, the disconnectionof a line or a loop or the substitution of a new line or loop for oneforming part of a, network. All of this may be performed by an attendantseated at a' switchboard. As pointed out above, since the leg of eachline and loop is equipped with its own'individual inverse neutralrepeater, these additions, subtractions and substitutions may be madewithout the necessity for making any compensating adjustments in thenetwork or in the-individual repeaters.

The invention may be more fully understood from the followingdescription when read with reference to the various associated drawingsin which:

Fig. 1 represents two four-wire full metallic telegraph line circuits,equipped with inverse neutral line repeaters, arranged for conversionfrom full to half duplex operation when connected to full or half duplexconcentration groups;

Fig. 2 represents two telegraph station loop circuits equipped with twoinverse neutral loop repeaters and two sets of loop concentration jacks,for connecting two local stations into a half duplex concentrationgroup;

Fig. 3 represents two line leg multiple circuits and two sets of lineconcentration jacks, the last mentioned for use in terminating twoflinesarranged for half duplex operation and includes a station calling-incircuit by means of which a station attendant may call an attendant at aservice board; f

Fig. 4 represents an idle indicator control circuit for controllinglamps whichmomentarily indicate all idle lines to remotey points, inresponse to the actuation of a key by an attendant who requires a newline. to enable the attendant to quickly select a line'to la particulardistant terminal for connection to a concentration group.

Fig. 5 represents a splitting circuit which is used with a telegraphcord circuit for testing lines before the lines are connected to aconcentration group;

Fig. 5A represents a telegraph cord circuit for use in connection withFig. 5 for testing lines before adding them to a concentration group;

Fig. 6 represents a local station connected through two separate loopsto two inverse neutra] loop repeaters and two sets of loop concentrationjacks, for use in full duplex operation;

Fig. '7 represents two leg multiple circuits and four sets of lineconcentration jacks for use in terminating two lines to remote terminalsarranged for full duplex operation.

The rectangle Fig. A bearing the-legend Half duplex concentrationgroupindicates the manner in which Figs. 1, 2, 3 and 4 are assembled to forma half duplex-concentration group, comprising two lines to two distantterminals and two local station loops, at the telegraph service board.

The rectangle Fig. B bearing the legend Full duplex concentration groupindicates the manner in which Figs. 1, 4, 6 and 7 are assembled to forma full duplex concentration group comprising two lines interconnectedthrough a telegraph service board, as the switchboard of this inventionis known to provide full duplex operation between two remote terminals.It shows also a single patrons station in the local area served by thetelegraph service board, connected through two loops into thefullyduplex line to provide full duplex operation between the localstation and the two remote terminals.

HALF DUPLEX CONCENTRATION GROUP A half duplex concentration group willfirst be described.

Figs. 1,-2, 3 and 4 are arranged in relation to each other as indicatedin the rectangular block diagram Fig. A, bearing the legend, Half duplexconcentration group. As thus arranged, they -constitute a concentrationgroup, comprising two telegraph line circuits and two telegraph loopcircuits, together with a calling-in signal circuit and an idleindicator control circuit. The telegraph line and loop circuits areconnected together at a telegraph central onice, through a new telegraphfacility to be known as a telegraph service board. The'v operation ofthe fundamental switching circuits of this new board are to be describedherein.

From the ofce where the telegraph service board is located, onetelegraph line circuit is assumed to extend to a telegraph centraloffice to the east and the second to a telegraph central oice to thewest. One loop connects a local telegraph station designated A, of afirst patron, in the same local area as that in which the service boardis located into the concentration group at the service board. The secondloop connects a local telegraph station, designated B, of a secondpatron, also in the same local area as that in which the service boardis located, into the same concentration group at the service board.

The circuits are arranged to form a half duplex telegraphconcentrationgroup. By this is meant, in this instance, that either loop station maysend telegraph signals which are transmitted to the other loop stationand over the line east and line west simultaneously, or either line maysend telegraph signals which are transmitted to each loop andv over theother line simultaneously. It is not possible, however, for any stationto receivefrom other stations while it is sending. i

In the description of a half duplex concentration group, apparatus inthe circuits for station A and the east line will be designated bynumbers only. -The letters B and W will be added to corresponding`apparatus in the circuits for station B and the west line respectively.

The manner in which a loop station transmits to the other loop and tothe two lines simultaneously will iirst be described. It will be assumedthat loop station A transmits. To do this the shunt 20|, whichshort-circuits the transmitting contacts-at station A when the circuitis idle, will be opened and the contacts of key 202 will be closed sothat the transmitting key 202 may take control of the circuit.

The armature of relay 2|2 is held in engagement with its left-hand ormarking contact by the eiect of current flowing from battery ZIB throughresistance 2H and the top winding of relay 2l2 to ground. No currentliows through the bottom winding of relay 2i2 for this condition as willbe explained below.

When the transmitting key 202 is closed, a circuit rnay be traced fromground through positive battery 203, through resistance 25M, throughresistance 205, through the bottom winding of reley 206,- through thetip and break contact of jack 201, through the break contact and ring ofjack 208, through the variable resistance 226, normal make contacts ofcall signal key 22T, through the winding of the sounder 209, through theclosed contacts of key 202, through the tip and break contact of jack208, through the break contact and ring of jack 20T, through the topwinding of relay 206, through the top winding of polar relay 2|0,through inductance coil 2H, v5 through the armature of relay 2|2,through resistance 2|3, through negative battery 2|4 and back to ground.Positive and negative battery are thus connected'to the two ends of theloop circuit and current flows, for the marking or "lvo closedcondition, through the loop circuit. The

eiect of the current flowing through the top winding of relay 2|0 tendsto actuate the armature of relay 2|0 to engage with its right-hand ormarking contact. It preponderates over the effect of current flowingthrough the bottom winding of relay 2|0, over a circuit from groundthrough negative battery 2M, through resistance 2| 3, through theleft-hand or marking contact and armature of relay 2|2, throughinductance coil 2| through the bottom winding of relay 2|0 andresistance 2|5 to ground, which current tends to actuate the armature ofrelay 2|0 to engage with its left-hand or spacing contact and thearmature of relay 2|0 is thus maintained in engagement with itsright-hand or marking contact.

Relay 206 is so arranged that when current flows through both its topand bottom windings, as is the case when the loop is closed, the eiTectin one winding is balanced by the eiect in the other winding and itsarmature remains in its normal unoperated position as indicated.

When the armature of relay 2|0 is in engagement with its right-hand ormarking Contact, it connects negative battery to the hub of theconcentration group. The circuit for this may be traced from battery 2|5, through resistance 2|8, through the bottom winding of relay 2 2,through the right-hand or marking contact yand armature of relay 2|0,through test resistance 2| 9, through the top back contact and armatureof relay 220, to conductor 22|. Conductor 22| may be consideredelectrically as a point which constitutes the hub of the circuit.

Station B is joined into the hub in a corresponding manner. For themarking condition, station B connects negative batteri/3. indicated 2MB,over a path similar to that traced for station A, which passesultimately through testing resistance 2 l 9B to hub 22 The manner inwhich one of the telegraph lines is connected into the concentrationgroup will now be explained. The circuit of the line east will be usedfor this purpose. This telegraph line is a four-wire metallic circuit.Its operation is described in detail in the application of R. B. Hearn,Serial No. 342,431, filed June 26, 1940, now Patent No. 2,259,637,granted Oct. 21, 1941. A s therein described, the circuit may bearranged to function either half duplex or full duplex dependent uponwhether it is connected into a full duplex or a half duplexconcentration group. In this instance it is connected into a half duplexconcentration group and therefore is arranged to function half duplex.

Refer now to Fig. 1 which shows in detail a four-wire metallic telegraphline connecting a distant telegraph central ofllce, located, it isassumed, to the east, into the concentration group at the oce where theconcentration group is established and which indicates diagrammatically,by a rectangular box, an identical telegraph line for the telegraph linewest which, it is assumed, connects a central oflice located to the westinto 75 the concentration group. Although a four-wire metallic circuitis shown for this purpose, carrier line circuits, one-way polarcircuits, and other line circuits, when terminated in proper inverseneutral type repeaters, may be used in place of the four-wire metallicline and the associated inverse neutral repeater shown.

The upper two line conductors of Fig, 1 constitute the path over whichthe distant repeater to the east receives from the concentration group.The lower two line conductors of Fig. 1 constitute the path over whichthe distant repeater to the east transmits into the concentration group.

Relays |0| and |02 are polar relays in the transmitting circuit at thedistant central oice. When the armatures of these relays arein thepositions indicated, which is for the marking condition, a path may betraced from ground through battery |03, through resistance |04, theleft-hand contact and armature of relay lill, through inductance coil|05, the top winding of polar relay |05, the armature and right-handcontact of relay |02 and' through resistance |07 back to ground.Apparatus corresponding to coils |24, |25 and |26 together with theassociated condenser |38 may be inserted, if desired, in this path atthe distant central terminal, in the same manner as they are connectedin the two top conductors of Fig. l. The function of this apparatus isto suppress noise caused by telegraph thump on the telephone circuitoperated over the same pair of cable conductors. The effect of thecurrent in the top winding in the path traced above is to operate thearmature of relay |06 into engagement with its right-hand or markingcontact. The operation of the circuit through the bottom winding ofrelay |06, known in the art as a vibratory circuit, is to tend to speedup the action of the relay. It is well known in the art and will not,therefore, be described herein in detail.

When the armature of relay |06 is in engagement with its right-hand ormarking Contact, a circuit may be traced from ground through negativebattery |08, through resistance |09, through the right-hand or markingcontact and armature of relay |06, through resistances ||0 and andthrough the top winding of polar relay ||2 to ground. The effect of thiscurrent is to actuate the armature of relay ||2 into engagement with itsright-hand or marking contact. No current ows through the bottom windingof relay ||2 for this condition as the circuit through the bottomwinding of relay ||2, connects at one end to the hub 22| of theconcentration group and at the other end to negative battery. Thiscircuit may be traced from negative battery H5 through resistances ||6and ||1, through the bottom windings of polar relays I8 and I9, throughthe lefthand armature and front contact of relay H3, through the bottomwinding of relay |2, through the right-hand front contact and armatureof relay I|3, through the right-hand or marking contact and armature ofrelay H2, through leg conductor |20, through Fig. 2 into Fig. 3 toparallel branches. One branch continues through the top armature andback contact of relay 30|, through test resistance 303 and the backcontact and armature of relay 304 to lthe hub 22| of the circuit. Theother branch extends in multiple through the tips of the multiple jacksSlt, 3H, 3 |8, etc., one of which is accessible at each position in thetelegraph service board of this invention.

A biasing circuit for relays 8 and I I9 may be traced from battery H5,through resistance |29 and the top windings of relays |I8 and H9 to.ground. The eiect of this current tends to actuate the armatures ofrelays ||8 and ||9 to engage with their right and left-hand contacts'respectively for the marking condition. This eiect is not opposed asthere is no current flowing through the bottom windings of these relaysfor the marking condition of the concentration group, since all of thelegs of the concentration group terminate in battery of thesame polarityfor the marking condition. v

The loop over which the distant office to the east receives may betraced from ground, through battery l2| to its positive terminal,through rei25, through the bottom line conductor to ther distantterminal, through the winding of the receiving relay |21, through thetop line conductor, through the top windings of the repeating coil |26,through the top windings of inductance colis |25 and |24, through thearmature and righthand or marking contact of relay i I8 and resistance|30 back to ground.

The four-wire line to the west indicated by the rectangular box at thebottom of Fig. 1 is arranged in the identical manner as that describedfor the four-wire line to the east. It connects negative battery of thesame magnitude as battery H5 in the east line through an identicalcircuit to leg conductor I3 which corresponds to conductor |20 of theeast line, through the top outer armature and back contact of relay SWand test resistance 303W, through the back contact and armature of relay304W to hub 22|.

Thus each line and each loop leg connects negative battery of the samemagnitude to the hub of the concentration group for the markingcondition.

If a spacing signal is transmitted from any station loop circuit or fromany telegraph line forming part of the concentration group, the leg ofthe circuit transmitting the spacing signal will be connected to groundwhich grounds the hub and operates a relay in each of the other legs totransmit the spacing signal into each of the other connected circuits.performed will now be explained.

It will be assumed that the operator at station A opens the contacts ofthe transmitting key 2&2V

to send a spacing signal. This breaks the loop circuit for station A,heretofore traced. The top winding of relay 2li! is deenergized. Thearmature of relay 2|0 is actuated, under the iniiuence of currentthrough its bottom winding, to engage with its left-hand or spacingcontact which is grounded. This disconnects negative battery 2|6 fromthe leg which extends through resistance 2 9 into the hub 22| andconnects ground through resistance 2|9 to hub 22|.

When ground is connected to the hub, a circuit may be traced from hub22| through the upper armature and back contact of relay 22GB, throughtest resistance 2 IEB, through the armature and right-hand or markingcontact of relay 2|0B, through the bottom winding of relay 2|2B andresistance 2|8B, to battery 2 ISB. The effect of this current flowingthrough the bottom winding of relay 2 |2B preponderates over the eiectof current iiowing through the top winding of relay 2|2B which has beenholding the armature of relay 2|2B in engagement with its left-hand orThe manner in which `this is marking oontactand theA armatureof relay2|2B is actuated to engage with its. right-hand or spacing Contact.

Loop B is arranged in the identical manner described for loop A. Whenloop A was traced it was shown that the two ends of the loop terminatedin vbattery of opposite polarity for the marking condition. Similarly,the two ends of loop B terminatein battery of the opposite polarity forthe marking condition. When, however, the armature ofrelay 2|2Bvisactuated 'to engage with its right-hand armature, negative battery isdisconnected from one end of the loop and both ends are terminated inpositive battery of the same magnitude so thatfno currentA flows in theloop. The sounder 209B Aat station B is deenergi'zed'and a spacingsignal is received at station B.

The manner in which thev same spacing signal is received at the eastcentral telegraph terminal will now be explained.

`When the spacing signal is received in the hub from station` A, ground,as has been shown, is connected through resistance` 2|9 to hub 22| and acircuit may be traced through the armature and back contact of relay 30dthrough testing resistance SH3, through the top outer back contact andarmature of relay 30|, through leg conductor |20, through Fig. 2 intoFig, 1, through the armature and right-handcontact of relay ||2, throughthe right-hand armature and front contact of relay H3, through thebottom winding of relay H2, through the left-hand front contact andarmature of relay I3, through the bottom windings of relays i lsand H8,through resistances l l and l It and battery l5 to ground. The effect ofcurrent flowing in the bottom windings of relays H9 and I|8`forthiscondition is such that it tends to actuate the armature ofrelay H9to engage with its right-hand contact and the armature of relay I8 toengage with its left-hand contact and this elect preponderates over theei'ect of the current iiowing through the top windings, so the armatureof relay |19 is actuated to engage its righthand contact and thearmature offrelay ||8 is actuated to engage tslleft-hancl contact.

When lthe armatures lof relays H9 and H8 are actuated as described inthe foregoing paragraph, the polarity of battery |2| in relation to thetwo ends of the east send line through the receiving relay at thedistant ofce will be reversed. That this is so may be understood byobserving that there are, two conductors extending from each ofresistances |22and |3 respectively. One conductor. extends from eachresistance to contacts which are in engagement with the armatures ofrelays H9 andl I8 when their armatures are in the positions shown inFig. 1 and one conductor extends from each of said resistances to acontact on the other of therelays with which each armature makesengagement when in the spacing condition. .Thus as the two relays |19and H8 respond to a spacing signal, the polarity of battery |2|connected to the ends of the line i'or the marking condition isreversed, resulting in a spacing signal being transmitted to the distantreceiving relay |21.

The spacing signal originating at station A is transmitted tothe'distant receiving relay connected to the west line in the samemanner as described above for the east line.

Thus as the armature of the relay 2|0, which receives from station A andtransmits toward the hub, is actuated so as to connect ground andnegative battery alternately to the hub 22|, the

armature of the receiving relay in the inverse neutral repeater of eachof the other legsrconnected to the hub, whether it be a loop leg or aline leg, is operated simultaneously to transmit spacing and markingsignals into its loop or line.

When signals are transmitted from a distant oiiice over a telegraphline, it will be assumed over the east line, relays and |02 in thedistant oirlce are operated from a connected circuit not shown. Thisreverses the connections between the two conductors of the bottomtwo-wire line and battery |03. Relay |06 is'in turn actuated. As thearmature of relay |06 is actuated between positive and negative battery,relay I I 2 responds. As the armature of relay ||2 is actuated, negativebattery and ground are alternately connected to hub 22| and marking andspacing signals are impressed upon all other legs forming part of theconcentration group.

In the same manner signals may be transmitted from the distant westernoilice rover the west line into its respective inverse neutral re.

peater and thence to the hub to actuate the send'- ing relay in eachindividual inverse neutral re-v Breaking operation in a duplexconcentration group It is possible to transmit a break signal from anycircuit connected into a half duplex concentration group, to prevent anycircuit which is transmitting to the other circuits of a concentrationgroup from continuing to transmit. The manner in which this is performedwill rst be described for the condition in which signals are beingtransmitted from the distant oillce over the east line and the attendantat loop station A breaks. f

When signals are being transmitted from the distant oce over the eastline, it has been shown that relays |06 and ||2 :follow the signals toconnect ground and negative battery alternately to hub 22 I. If theattendant at station A wishes to stop the transmitting from the eastline, so that station A may transmit, key 202 is opened and ismaintained in the open condition. The opening of key 202, as has beendescribed, results in ground being connected to the hubwhen relay 2 I 2next closes its marking or right-hand contact. Since the key 202 ismaintained open, a permanent ground is connected to the hub resulting ina permanent spacing signal being transmitted from the hub out over eachconnecting leg. In the case of the line which is receiving signals fromthe distant oice, if the yarmature of relay I I2 is in engagement withits left-hand or spacing contact, in response to a spacing signaltransmitted from the east line toward the hub, nothing will happenmomentarily in its send side, as ground from the hub will be connectedto one end of conductor |20 and it will meet ground on the left-hand orspacing contact of relay I|2. As soon as the armature of relay II2 isactuated to engage with its right-hand Contact, however, the ground fromthe. hub will be connected to one end of the path through the bottomwindingsrof sending relays |I9 and II8 and battery II5 will be connectedto the other end over the circuit heretofore traced. Under thiscondition the armature of relay I2 is maintained in engagement with itsright-hand contact, as the effect of the current flowing through thebottom winding of relay I I2, tending to actuate the armature of relay II2 toward the right, preponderates over the effect of spacing signalcurrent from relay |06 tending to actuate the armature of relay I|2toward the left. Relays IIS and ||9 will be operated when the armatureof relay II2 is on its right-hand contact, from ground connected to thehub. With the armatures of relays II8 and IIS actuated to their spacingcontacts, a permanent spacing signal is transmitted toward the distantcnice to the east as a breaking signal.

If either loop stat'ion is transmitting, any line or the other loop maybreak. l't will be assumed that station A is transmitting and that theeast telegraph line breaks. This is performed in the following manner. Apermanent spacing signal is transmitted from the east telegraph terminalinto the hub, operating relay |05 to its left-hand or spacing contact.This will operate relay II2 to spacing when relay 2I0 next closes itsright or marking contact to remove ground from hub 22 i. This results inthe connection of permanent ground to hub 22| from the left-hand contactand armature of relay ||2. A circuit may be traced from the grounded hub22|, through the armature and back contact of relay 220, throughresistance 2li), to the armature of relay 2I0. If the armature of relay2I0 is again in engagement with its left-hand or spacing Contact,nothing happens momentarily. When the armature o1 relay 250 next engagesits right-hand contact, the circuit will be extended through the bottomwinding of relay 2 I2 and resistance 2 I8 to battery 2I6. This operatesthe armature of relay 2I2 so that its armature engages its right-hand orspacing contact. This disconnects negative battery 2N2 from one end ofthe loop through station A and connects both ends of the loop topositive battery 203. This results in a permanent spacing signal beingtransmitted over the loop which is received by sounder 209 at station Aas a breaking signal.

As a general proposition, it may be stated that, when inverse neutralrepeaters are interconnected, a spacing signal transmitted toward thehub, by any repeater connected to the hub, will result in the connectionof ground to the hub and' a spacing signal will be transmittedsimultaneously from the hub through all of the other repeaters connectedinto the hub, and further, a permanent spacing signal transmitted fromany repeater while another repeater in the concen tration group istransmitting toward the hub, will result in the loss of control, by thestation which is transmitting, of the relay in the repeater whichtransmits toward the hub, when the station which is transmitting nextsends a marking signal toward the hub. The relay which transmits towardthe hub will then be held to marking and simultaneously the permanentspacing breaking signal will be transmitted to the station which wastransmitting.

Circuit for permitting station connected into a half duplexconcentration group to call switchboard The arrangement of Figs. 1,2, 3and 4 per Fig. A is equipped with a calling-in signal by means of whichany loop station connected into the concentration group may signal theattendant who is administering the concentration group at the serviceboard.

The three jacks associated individually with each station loop and eachtelegraph line in any particular concentration group are all located inthe same attendants position at the service board. The service board isa multiposition board. Various concentration groups are administered atvarious positions. The attendant in charge of a particular positioncontrols a certain number of concentration groups such as theconcentration group per Fig. A, comprising Figs. l, 2, 3 and 4.

The manner in which an attendant at a station, such as station A, maysummon an attendant at the position in the service board where theconcentration group is being administered is as follows.

The attendant at station A grounds one side of the station loop circuit.This may be done by momentarily actuating the call signal key 221 inFig. 2, which rst grounds the lower loop conductor through the set andopens the upper loop conductor.

When the station loop circuit is closed, the effects of the currents inthe top and bottom windings of differentially connected relay 206neutralize each other, so that the armature of relay 206 remains in thecondition shown. During the transmission of a spacing or a break signalfrom station A, when the loop is opened, no current flows through eitherwinding of relay 206. No current flows when a spacing signal istransmitted toward station A as both ends of the loop are connected tobattery of the same polarity and magnitude for this condition. When thelower loop conductor is grounded and the upper loop conductor is opened,however, a circuit may be traced from ground through sounder 209, makecontact and armature of key 202, through the tip and break contact ofjack 208, the break contact and ring of jack 201, the top winding ofrelay 206, the top winding of relay 2I0, inductance coil 2| I, thearmature and left-hand Contact of relay 2I2, resistance 2|3 and battery2 I4 to ground, operating relay 206. With relay 206 operated, a circuitmay be traced from ground through the armature and front contact ofrelay 206, the bottom armature and back contact of relay 220, conductor222, which may be considered electrically as the hub of the calling-incircuit into Fig. 3, conductor 305, the back contact and armature ofrelay 306, through the winding of relay 301 to battery, operating relay301 which locks from its bottom contacts under control of relay 306. Theoperation of relay 301 connects battery through the top armature andfront contact of relay 301 through the iilament of lamps 308 and 309 inparallel to ground, lighting both of these lamps as a signal that somestation associated in the concentration group is calling in. One ofthese lamps, such as the primary appearance lamp 308, is located at thesame position as the one in which the loop and line concentration jacksof the concentration group are located. The secondary appearance lamp309 is located at an adjacent position to provide the advantage ofteamwork since with this arrangement any of four service boardattendants may answer the call through the associated jacks.

Any other station, such as station B, connected through a station loopinto the concentration group may light the same lamps 308 and 300 by anoperation similar to that described for station A. This should beapparent from reference to the station loop and loop repeater forstation B. Ground from thearmature of relay 206B is connected throughthe bottom armature and back contact of relay 220B to conductor 222 inparallel with the ground from relay 206.

In response to the lighting of the lamps 308 or 300, the service boardattendant administering the concentration group may connect anattendants telegraph transmitting and receiving set circuit operating onthe inverse neutral principle to jack 3I0 or jack 3| I. This connectingcircuit will `not be described in detail hereunder as it does not formpart of the present invention. At this point attention is called to thefact that battery connected to the sleeve of the attendants circuitoperates relay 306 over an obvious path. .The operation of relay 306breaks the operating path heretofore traced for the operation of relay301 and relay 301 releases, extin guishing the lamps. The hub of theconcentration group, conductor 22|, is connected in multiple to the tipof jacks 3I0 and 3II to provide a connection for the transmitting leadin the attendants circuit. By means of inverse neutral repeaterconnected to the tip of jacks 3| I, it is. possible for the attendant totransmit and receive signals to andY from the various stations and linescomprising the concentration group or to monitor on all signalstransmitted through hub 22|.

The rings of jacks 3I0 and 3II are connected in multiple to the commoncalling-in or signal hub conductor 222. This is to provide a recallfeaturein the attendants connecting cord. A recalling operation isperformed at a station in the same manner as a calling-in operation. Ifan attendants cord circuit is already connected to either jack 3I0 or3|I andany one of the stations connected into the concentration groupthrough a station loop repeater wishes to again summon the attendantsattention, the lower station loop conductor is grounded. This connectsground, in the manner already described, to conductor 222 and to thering of both jacks 3I0 and 3|I. This ground operates a relay in theattendants cord circuit connected to either jack V.to light asupervisory lamp as an indication that a station is recalling.

Connecting supervisor circuit and other circuits to concentration groupJacks 3I0 and 3II also provide means for establishing a connection -to asupervisor. By means of a patching cord circuit it is possible toconnect a test signal supply circuit to the concentration group throughjacks 3I0 and 3| I. Also, jacks 3I0 and 3l I may be used with suitableconnecting circuits for the measurement of bias or distortion.Y

Releasing a line from a. half duplex concentran tion group Because eachtelegraph line to a distant city and each telegraph loop to a localstation appearing in the telegraph service board is terminated in'itsown individual inverse neutral repeater, it is possible in the systemdisclosed herein to make changes in a concentration group such asremoving lines or loops, adding lines or loops or substituting lines orloops, without the need for making compensatory adjustments in the legside of any repeater to accommodate the change. The invention hereinpermits these changes to be made flexibly at the switchboard positionwhere the concentration group is administered. with a minimum of eiorton the part of a service board attendant.

It is necessary on occasion to make temporary changes in a concentrationgroup, such as to replace a line or loop which may be defective or toprovide additional acilitites in a concentration group such asadditional lines or loops, or to remove a line or loop at thetermination of its daily service period. The manner in which a telegraphline is disconnected from a concentration group will now be explained.The east line will be used for the purpose.

To perform this operation a control plug, such as plug 3|2, having itsring and sleeve conductors interconnected, is inserted into acooperating jack, such as release control jack 3|3. This connects thering and sleeve of jack 3|3. A circuit may then be traced from ground,through the middle winding of relay 35, to the sleeve ol' jack 313,through the sleeve of plug .3|2 to the ring oi plug 32, through the ringof jack 313 and the top winding of relay 3|5, vthrough battery 3M backto ground, operating relay. 3|5. The operation of relay 3|5 connectsground through its upper armature and front contact and the winding ofrelay 30| to battery, .operating relay 30|. The operation of relay 30|breaks the connection between the leg conductor 20 and the hub 22| aspreviously traced, thus disconnectingthe east line from theconcentration group. The operation of vrelay 30| also breaks theconnection which extends from battery through the winding of relay |13in Fig. l, and conductor IM, into Fig. 3, through the bottom middlearmature and back contact of relay 30| and the top back contact andarmature of. relay 302 to ground, thus disconnecting ground formerlyfurnished through the top armature and back contact of relay 302. RelayH3 releases. rThis places the inverse neutral repeater in the east linein its normal condition which is the full duplex condition.

It has been explained that the circuit per Fig. l may function eitherfull duplex or halfk duplex dependent upon whether it is connected intoa full duplex or half duplex concentration group. When it was connectedinto the half duplex concentration group as explained above, it wasconditioned to function half duplex through the operation of relay H3.Now that it has been released, the repeater is restored to its normaliull duplex condition. Even though it is no longer serving in theconcentration group described above, it may be appropriated for use withanother concentration group which may operate full duplex or halfduplex. If the new concentration group is to operate full duplex, relayH3 will remain unoperated.` If the new concentration group operates halfduplex, relay H3 will be again operated.

To return to the operation of relay 30|, its operation sends a permanentspacing signal to the distant eastern terminal. This .is performed asfollows. A circuit may be traced from ground through the armature andback contact of relay 302, through the top inner front contact andarmature of relay 30|, through conductor |32, through the left-hand backcontact and armature of relay H3, which is now released, through thebottom windings of relays H9 and H8, through resistances, Ill and IIBand negative battery ||5 back to ground. This operates relays ||9 and||8, reversing the polarity .of battery |2| as connected to the sendingline and tant eastern terminal.

The operation of relay 30|, also, by the transfer of its bottominnermost armature from its back to its front contact, disconnectsground from the sleeves of the multiple jacks 3|6, 3|? and 358 andconnects the sleeves of these jacks to battery through the windings ofrelays 302 and 3110. The object of the connection of ground to thesleeve while the line is connected into a concentration group was topermit monitoring on the circuit through a multiple jack. The plug of amonitoring circuit may be inserted into a multiple jack at any positionin the board and ground on the sleeve of the multiple jack operates arelay in the monitoring circuit which conditions the monitoring circuitfor monitoring. The purpose of the change from ground on the sleeve tobattery through the relays will be un derstood from the descriptionbelow.

The operation of relay 30| performs one other switching operation. l'textends a circuit, which may be traced from ground, through the filamentof lamps 32|, 32,2 and 323 in parallel, through the bottom outermostfront contact and armature of relay 30|, through the bottom back contactand armature of relay 302 and through conductor 320 to a front contactof relay 40| in Fig. 4 which forms part of the idle indicator controlcircuit which will now be explained.

Idle indicator control circuit for indicating Zine available forconnection to concentration group It has been explained that eachtelegraph line connecting the service board to a distant city, Whetherconnected into concentration jacks at a particular attendants positionor not, is extended through a group of multiple jacks throughout theswitchboard line-up. Some means must be provided for distinguishingbetween the lines which are serving as part of an operatingconcentration group and those which are available to be connected into aconcentration group on a temporary basis by means of a patchingoperation. A line may be connected into a concentration group or it maybe released from, or not connected to, a concentration group forrelatively long intervals. If a lamp were lighted throughout eitherinterval as an indication of the condition, it would mean that manylampsk would be burning in the switchboard at all times. This has anumber of disadvantages including battery drain, reduced life of lampsand reduced contrast between lighted and unlighted lamps, such asstation calling-in signal lamps 308 and 309 described above.

In order to provide the advantages of a normally unlighted switchboard,and the other advantages enumerated above, the idle indicator controlcircuit is furnished. Its function is to light the lamps associated withall idle telegraph lines to distant cities momentarily, in response tothe actuation of a key by an attendant who requires such a line, so thata selection of a line to a particular city may be made if such a line isavailable.

If an attendant at a particular position in the telegraph service boardline-up requires a telegraph line to a distant city and wishes to knowwhich lines are available so that he may make a selection, the attendantoperates a key such as 402, Fig. 4, at the particular attendantsposition. There is one such key at each position in the line-up. Keys atother positions are indicated by keys 403 and 404. When key 402 isoperated, relay 005 is operated over an obvious circuit. The voperationof relay 405 closes a circuit Vfrom ground through the bottom frontcontact and armature of relay 405, through the Vwinding of relay Llliand resistance @lil through battery to ground. Relay 465 will operateand lock up through its top middle front `contact and armature toground. The operation of relay it will connect ground through itsAbottom inner front contact and armature and the winding of relay lillto battery, operating relay till. The operation of `relay MI willconnect battery through its various contacts in parallel to a number ofconductors extending to various leg multiple circuits. Each of saidconductors is arranged so that it may be `multipled to a number of legmultiple circuits. A circuit may be traced from battery through the toparmature and front Contact of relay dill, through conductor Stil,through the bottom armature and back contact of relay 362, through thebottom. outermost ar mature and front contact of relay 3M and throughthe filaments of lamps 32l, and 323 in parallel to ground, lighting eachof the lamps, as an indication that the telegraph line circuit to adistant city associated with these lamps is available for use. Onlysuch. circuits as are available for use will have their associated idleindicating lamps lighted as the path to the lamps inthe case of circuitswhich are not idle will 4not be closed.

The lamps indicating that a circuit is available for use remain lightedfor a short interval only, while a selection of one of them-is beingmade and then the lamps are extinguished through the operation of theidle indicator control circuit. The manner in which this is performedwill now be explained.

When relay M6 is operated a circuit may be traced from plate batterySL38 through resistance 409 and conductor dill, through resistances Alland M2 in parallel, through the bottom armature and front contact .ofrelay Mid, through the filament of vacuum tube M3 and resistance 4M toground, lighting the ilament. After a momentary interval key M2 isreleased, in lturn releasing relay ill. This removes ground which hasbeen connected through the front contact and top armature of relay 95 tothe upper terminal of condenser M5 and condenser lid is charged .over apath from battery Mil through resistance 399, through resistance M5 thetop innermost armature and front Contact of relay 406 to the upperterminal of condenser M5, the bottom terminal of which is grounded. Whenthe top plate of condenser @l5 and the grid of tube M3. connected inparallel with the top plate of the condenser, have assumed a properpositive potential with respect to the cathode of tube M3, current williow through the plate circuit of the tube from positive battery limi,through resistance 4.99,. through the winding of relay lll to the plateof tube fila, from the `plate to the filament of tube H3 and throughresistance lid to ground, operating relay fili, The magnitude ofresistance M5 and the capacity of condenser H5 establish the intervalnecessary to charge condenser H5 to the proper positive potential andthe interval been established for use with the idle indicating lamps ofthe inverse neutral circuits at approximately six seconds.

When relay lil is operated, ground is connected to the leit-handterminal of resistance fili?. This shortcircuits the through the windingof relay E-ili to ground, releasing relay The release of relay ME breaksthe path heretofore traced through the filament of tube ll-li. The

release of relay 656 also disconnects battery 353 'from the top terminalof condenser ll i il. The battery connection of the condenser will bereplaced by direct ground through the top outermost armature and backcontact of relay 46S which will discharge condenser M5. When thefilament of tube M3 is extinguished current will no longer flow throughthe tube and relay lill will be released. The idle indicator controlcircuit i is thus returned to normal.

If at any time a key such as w3 is operated momentarily, in turnoperating relay 405 before the timing circuit has been permitted tocomplete its cycle, condenser M5 will be discharged from groundconnected to the top front contact and armature of relay lli and theentire timing cycle will be repeated.

Replacing a Zine forming port of a half duplex concentration group witha Zine which has been released from a dilierent concentration group Theconcentration group is arranged so that a line forming part of aconcentration group may be replaced by a second line. This second linemay be a line which has been released from another concentration groupor it may be a spare line. A spare line is one which is not normallyconnected into a concentration group, a spare line terminates inmultiple jacks and a leg multiple circuit, but it is not provided with agroup of three concentration jacks and connected into a hub as is a linewhich is arranged to normally form part of a concentration group. I

In this section the operation of replacing a line in a concentrationgroup by a line which has been released from another concentration groupwill be described.

In order to replace a line forming part of a concentration group with anew line which has been released from a concentration group and istemporarily idle, rst the idle indicating circuit described in theforegoing is operated, so that an idle line to the proper distant citymay be indicated, if one is available, in order that the idle line maybe selected for use. If such a line is available, the attendant, bymeans of a patching operation, through the leg patching cord circuit,shown at the right of Fig. 3, will connect the new line to theconcentration group and, as a result of the patching operation, the oldline will be automatically released from the concentration group and thenew line will function in its stead.

For the purposes of this explanation, it will be assumed that the lineWest has been previously .released from another concentration group inanother position of the board and it will be assumed that it connects atthe distant end to the desired distant termination. The line West willbe used to replace the line east.

Plug 324 will therefore be inserted into jack lW when lamp SZIW lights,indicating that the line is idle. Plug 325 will be inserted into jack 3I3. A circuit may then be traced from battery through the windings ofrelays 383W and SQZW in series, through the bottom innnermost frontcontact and armature of relay 3lilV7, relay SllW being operated while aline is released, through the sleeve of jack MSW, through the sleeve ofplug 32d, sleeve of plug 325, sleeve of jack EL3 and the low resistancemiddle winding of relay 355 to ground. Relays 399W and 302W operate inseries with the low resistance middle winding of relay SI5. Relay 355operates. The operation of relay M5 in turn operates relay Sill. The

operation of relay breaks the leg path from the east line repeater intothe hub 22| of the concentration group, disconnecting the east line fromthe concentration group and performs all of the other operationsheretofore described attending the operation of this relay.

The leg of the new line repeater is connected through the tip of jack3I6V, tip of plug 324, tip and break contact of jack 326, tip of plug325, tip of jack 3|3, test resistance 3D3, break contact and armature ofrelay 3M into hub 22! to incorporate the line West into theconcentration group.

It was pointed out that relays SISW and 302W operated in the west linewhich has replaced the east line in the concentration group. Theoperation o'f relay 3|9W connects ground to conductor IMW which extendsinto the winding of a relay in the West inverse neutral repeatercorresponding to relay H3, which conditions the west repeater tofunction half duplex in the same manner as described for the eastrepeater. Relay 302W in operating in the new leg multiple circuit forthe new line opens the idle indica-ting circuit for the West line as theWest line has now been appropriated and disconnects ground from the legof the repeater removing the permanent spacing signal which wastransmitted to the distant Western terminal while the line was idle. Theoperation of relay 302W also locks relay 3|5W from ground through itstop armature and front contact to hold relay 315W operated. The reasonfor this is that the west line was made available for use by a releasingoperation, such as just described above, or by means of inserting acontrol plug into a control jack, as previously described. Thisoperation is performed at another position in a jack corresponding tojack 3| 3W, namely at the particular position where the concentrationgroup With which the West line is assumed to be normally associated isadministered, The removal of the releasing plug would release relay 3l5Wand reconnect the west line into the concentraion group With which it isnormally associated. This is prevented by the locking of relay 3|5W whenrelay 382W operates.

The foregoing explains how a line released from the concentration groupwith which it is normally associated may be appropriated by an attendantto replace a line normally forming part of another concentration group.

The manner in which a line which is normally spare, as distinguishedfrom a line which is released from a concentration group with which itis normally associated, is connected into a half duplex concentrationgroup as a substitute for a line forming part of a half duplexconcentration group will now be explained.

Replacing a Zine forming part of a half duplex concentration group witha, spare Zine As stated above, spare lines are distinguished from linesordinarily forming parts of concentration groups, in that spare linesappear only in multiple jacks at each attendants position and are notextended through their leg multiple circuits into three individualconcentration jacks at a particular position, through which they areextended to a hub so that they normally form part of a particularconcentration group. A spare line may be appropriated, by means of apatching operation from one of its multiple jacks, at any position, to aparticular jack in a line normally forming part of a concentrationgroup, to replace a line normally forming part of a concentration group.

In order to replace a line normally vforming part of a concentrationgroup With a spare line, a patch is made from a multiple jack of thespare line to the control jack of the line which is to be replaced.

For purposes of this explanation it will be assumed that the West lineis now a spare line. In order that the west line may simulate a spareline, it will be assumed that its relay 30|W is permanently operated.Each spare line through,- out the board is arranged so that electricallyit is the equivalent of a line which normally forms part of aconcentration group, except that each of the circuits extending throughthe various armatures of its relay correspondingv to relay 30IW isclosed through its respective front contact instead of through its backcontact as shown for the normal unoperated condition of relay 3DIW inFig. 3. Further, a spare line is not provided with a concentration jackcircuit.

It will be assumed that the spare West line is to be used to replace theeast line which normally forms part of a half duplex concentrationgroup. First the idle indicator circuit is operated and a lamp such as32|W is lighted indicating that the line is available. The plug 324 isinserted into jack 3|6W and plug 325 is inserted into jack 3I3.

As a result of this operation the tip of the spare line is extended intothe hub of the concentration group in the same manner as describedabove. The sleeve of the spare line is extended over a circuit, exactlythe same as described before, for a released line, starting from batteryconnected to relay 3l 9W in the spare line and ending in groundconnected to relay 3I5 in the replaced east line. Relays 3|9W, 302W andSI5 are operated in series. Relay 3|9W in operating conditions therepeater in the West line to function half duplex as describedheretofore. Relay 302W in operating disconnects the idle indicatingcircuit at its bottom armature and front contact. The operation of relay302W also operates relay 3|5W as described above, but this performs nouseful function in the case of a spare circuit, as it did in the case ofa. released circuit described above. The operation of relay 3| 5releases the replaced line from the concentration group.

Adding a released Zine to a half duplex concentration group It will nowbe assumed that the west line has been released from a concentrationgroup at another attendants position and that it is to be added to theconcentration group comprising the east line instead of replacing theeast line.

It should be remembered that a plug such as 3|2 is inserted into a jacksuch as 3I3W in the attendants position, where it is assumed that thewest line is normally associated into another concentration group. Thisoperates relay 315W in turn operating relay 30|W in the mannerheretofore described.

The attendant who desires to add a line operates the idle indicating keyat the position Where the concentration group to which the line is to beadded is administered. Once again the idle indicating lamps of allavailable lines are lighted.

`In order to add the West line to the concentration of which the eastline forms a part, the attendant inserts plug 324 into line multiplejack vwith a released line or afspare line.

. line is a spare line.

315W Whenlamp 321W lights. Plug 325 is inserted into jack 321.

VAs a result of this operation the tip of the west ner heretoforedescribed, through the sleeve oi i jack 3I6W, sleeve Vof plugs 324 and325 and sleeve of jack 321 to direct ground. This operates relays 3I9Wand 3(32W which conditions the West line for vhalf duplex operation,disconnects the idle indicator lamp circuit and provides `ground -tohold `relay 3l5W operated in the same manner as heretofore described.

It should be observed `that in the operation o1 adding a line, adifferent jack in the line concentration jack circuit normally formingpart oi `a concentration group is used than the jack which is used forreleasing a line or -for replacing a line forming part of aconcentration group All of these latter operations involve a releasingoperation, which must be performed by connection to -a jack such as 313vwhich controls the operation of the releasing `relay such as 3&5. Whenaline is to be simply added to a concentration group, connection isvmade to :jack such as 321 and --the releasing relay remains unaffected.

Adding a `spa-re .line 4to .a half duplex concentration group A spareline may be added to a concentration group. It will be again assumedthat the west That is, it is not provided with a group of individualconcentration jacks and its relay SiilW is blocked operated,

The attendant, at the position Where the concentration group to whichthe spare line lis to be added is administered, operates the idleindicator control circuit and, when all of the lamps associated withidle lines light, selects the spare west line tration group of which theeast line viorrns a part.

Plug 324 is inserted into jack 313W 'and plug 325 is inserted into jack321 of the east line. The tip of the west line is connected. into thehub over a circuit heretofore traced. Relays :3! 9W and 3il2W operatevin the same manner and perform the same functions as described above.The west line thus becomes a part of the concentration group with whichthe east line is normallyassociated.

Supervision in half dupler patching operations assumed that the eastline Ais `a spare :line in the idle condition and that a permanentspacing condition is imposed on vit at the distant ter minal.

In such cases, when -an idle indicating lamp lights in response to theoperation of a key such for addition to the particular concen- .as lm2by .an attendant who is y.seeking an available line to a particulardistant city, a patch is `not made immediately to ia concentrationgroup. Instead the attendant inserts the plug 50| of a `telegraph cordcircuit, indicated `as Fig. 5A, into jack `5&2 of the splitting circuitof Fig. 5. The telegraph cord circuit per Fig. 5A is not shown in detailin this application as it is not a part ,of this particular invention.The attendant also inserts plug 324 rinto a multiple jack, such as 315and plug 325 into jack 5o3 of Fig. 5. With these circuits interconnected`in this manner, the Vconductor over which communication signals arereceived over the line circuit incoming from the distant office isextendedthrough the tip of multiple jack 3|6, tip of plug 32d, tip andbreak contacts of jack 32S, tip of plug 325, tip of jack Itii'ii, 'tipyoi jack A582, tip of plug 55! and into the telegraph cord circuit,Where it passes ultimately through the winding of a telegraph receivingrelay such as 5&1, to negative battery. At `the saine time ground isconnected through vthe sleeve of jack A5il3, sleeve of plug 325, sleeveof plug sleeve of jack '316, through the'bottom innermost contact ofrelay V30| which is operated, and the `vvindings .of relays 392 and 3l!)to loattery. Relays 3l@ and 332 operate from the direct ground on thesleeve of jack 503. This operation of relay 382 removes ground from thepath heretofore traced through the windings of relays H9 yand 153 tonegative battery H5. This results in the removal of the Apermanentspacing signal which was being transmitted to the distant terinitialover Vthe east rline Aand a change of relays iii) ,and :llt `to marking.The operation of relay '3&9 operates relay H3 which changes the linerepeater from the full duplex to the vhalf duplex condition.

When the marking signal is received at the distant terminal, theattendant thereat may respond .in such manner that the permanent spacing:condition Yimposed rat the kdistant oilice on relays iii! and H32 isrernoved and changed to marking. As a result of this, relays Hi8 and H2mi. are .in turn 4changed to the marking condition.

When ground is removed from the armature of relay iii, the permanentspacing signal is re- ;nioved 4from conductor |20 and the tip circuitheretofore traced into fthe telegraph cord circuit. When. :the receivingrelay i591 connected Ato the :tip circuit responds to the markingsignal, the yattend ant `knows that the east line may be connect-ed4into `the concentration group, or he may communicate with the distantattendant and cooperate in making any tests necessary to assure propertransmission of the line and associated repeaters. The attendantthereupon disconnects lplug '325 from `jack 553 and connects it insteadinto ajack vin a line circuit of the concentration group such as jack313W or v321W depending upon Whether the line is to replace an existingline in a concentration group or be added to a concentration group.

Releasing u station Vcircuit from a. half duplex concentration groupStatic-n loops normally connected to a concentration group :may bereleased from the concentration group for test purposes, or for transferto other `concentration groups or because their daily working period isended. To perform this operation, a plug such as SI2 having its ring andsleeve conductors interconnected is inserted in a .lack such as 22d.

A circuit path is established as a result .of the above operationextending from ground, through the sleeve of jack 224, sleeve of plug3I2, ring of plug 312, ring of jack 224 and bottom winding of relay 220to battery, operating relay 220. The operation of relay 220 disconnectsthe station vfrom the concentration group, by disconnecting the looprepeater transmission lead from the hub 22| at the top armature and backcontact of relay 220 and disconnecting the loop calling-in lead at thebottom armature and back contact of relay 220.

Adding a station circuit to a half. duplex concentration After a loophas been disconnected from a concentration group it may be added to adifferent concentration group by inserting the plug v324 into a jacksuch as 225 and the plug 325 into a line jack such as 321. This extendsthe tip or transmission conductor of the loop repeater through the tipof jack 225, tip of plug A324, tip and break contact of jack 326, tip ofplug 325, tip of jack 321, into the hub 22| of the concentration group.It also extends the loop .repeater calling-in conductor through the ringofiack 225, ring of plug 324, make contact of key 333, which is operatedfor this pulpGSe, ring f plu-g 325, ring'of jack 321 into the commoncalling-in conductor or signal hub 222.

While a station loop repeater is released, connection may be made tojacks such as 225 for testing purposes. This provides access to both thetransmission conductor and the calling-in conductor of the looprepeater. Ground on the sleeve of the jack 225 is provided forcontrolling relays in the sleeves of cooperating testing cord 'or jackcircuits.

Transmitting good night or permanent spacing signal When a station looprepeater is released, it may be arranged to transmit a permanent spacingor good night signal toward the station by inserting a control plug suchas 328 into a jack such as 225. This connects ground from the sleeve ofjack 225, sleeve of plug 328, tip of plug 329, tip of jack 225 to thetransmission conductor of the loop repeater which transmits a permanentspacing signal to the station.

If it is desired to transmit a good night or Further, since the tip ofjack 321 is common to the hub, a monitoring circuit, not shown, may beconnected to jack 321 and signals may be received in the monitoringcircuit from the hub over the tip of jack 321 and through the tip of theplug of the monitoring circuit.

Provision for testing and observing hits on a leg in a half duplexconcentration group Jacks 223, 223B, 329, 329W and 326 provide means forconnecting a testing circuit to a line or loop leg and testing itseparately from the concentration group and for observing for hits by4means of a trouble indicator'cord circuit, not

tor cord circuit to jacks such as 329, 223 or 326 will permitobservation for hits occurring on the associated leg. When a line orloop leg is added to a concentration group through the medium of thepatching cord terminating in plugs 324 and 325, such observations Willbe obtained through jack 326.

Attention is particularly called to the resistances 2l9 and 2|9B in Fig.2 and 353, 303W and 333 in Fig. 3. One end of each of these resist'-ances is connected to a tip conductor of one of each of the above jacks;The opposite end of each of these resistances connects through thecontacts of the test relay to a ring conductor of the correspondingjack. These resistances are connected in series in the leg lead in eachin'- stance. When signals are being received from a leg, a potentialdrop in a particular direction occurs in its associated resistance. Whensignals are being sent to the'leg through the resistance, the drop is inthe reverse direction. Further, when signals received from one leg aresent to a group of legs associated together in a concentration group, agreater' current ows in this leg than when it is sending to a line orloop. The drop for the first of these conditions is therefore greater.This assumes that at least three repeater legs are joined in aconcentration group. `If a linear loop is in trouble, so that it iscausing random false spacing signals to be'transmitted toward the hub,this condition may be detected by connecting to jacks, such as 223,223B, 329 and 329W, a device which is responsive to changes of potentialacross two points and which discriminates between such changes inreverse direction.

Relays 220, 229B, 394, 304W, and 334 each have a Winding connectedbetween ground and the sleeve of an associated jack.` These relays arearranged so that they may be operated or remain released, depending uponthe resistance inserted in the connection to battery in the sleevecircuit of the cooperating cord circuit. When a troubler indicator cordcircuit is connected toany one of the jacks for the purpose of observinghits on the associated leg, since the trouble indicator cord is arrangedto respond to a drop across the test resistance in a particulardirection, the resistance must remain in circuit and the test relayremains unoperated.

Jacks 223, 223B, 329, 329W and 326 also provide means for monitoring onor communicating over a concentration group. The ring of each of thesejacks' connects directly to the hub of the concentration group. Aninverse neutral repeater terminated in a receiving device only formonitoring, or in a sending and receiving device combined forcommunication, may be connected by means of a plug to the ring conductorof each of these jacks. Under these circumstances, if it is desired tomonitor on the Whole concentration group or communicate over the wholeconcentration group, the resistance of the connected sleeve circuit Willbe high to prevent the operation of the relays, such as 22D, 304 and334.

If it is desired to split the leg of a loop or a.

line oif from a concentration for testing it sep-l arately, connectionis made to jacks such as 223, 329 and 32B and the sleeve of theconnecting circuit 1s arranged so that it connects to battery through alow resistance to permit test relays such as 220, 304 and 334 tooperate. This disconnects the associated leg from the concentrationgroup. The leg is extended through the associated tip conductor and thehub 22| through the associated ring conductor of the cooperating jackinto the connected circuit for testing. By connecting the inverseneutral repeater in the cooperating connected circuit through asplitting key, it is possible to communicate with the leg which has beencut oi from the hub over the tip or with the circuits which remainassociated in the concentration group over the ring of jacks such as223, 329 or 32S.

FULL DUPLEX CONCENTRATION GROUP A full duplex concentration group willnow be described.

In a full duplex concentration group, separate independent hubs arerequired for transmission in opposite directions. The sending loops,receiving loops and lines may be connected together in various ways,depending upon the trafc requirements. The arrangement to be describedwill therefore be a typical arrangement. In this typical arrangement, atelegraph service board will be used to interconnect an east line, awest line and a local patrons station. Full duplex service is providedbetween the east terminal and the west terminal over the east and westlines in tandem. The patrons station is equipped with two loops for fullduplex operation.

For full duplex operation, Figs. l, 6, '7 and 4 are arranged asindicated in the rectangular box Fig. B, bearing the legend Full duplexconcentration group. including two lines and a local station comprisingtwo loops. The two lines may be assumed to be an east line, whichextends to a distant eastern terminal, and a west line which extends toa distant western terminal.

Although the detailed description will again assume the use of four-wiremetallic line circuits, it should be understood that carrier linecircuits, two path polar circuits or differential duplex line vcircuitsmay be used When terminated in the proper inverse neutral type ofrepeater which provides separate send and receive legs onl the dropside. The legs appear in leg multiple circuits as previously describedand each leg is extended from the leg multiple circuit through a lineconcentration jack circuit to a hub. The sending leg of one line isconnected through the hub to the receiving leg of the other line in eachinstance.

Since two hubs are required in full duplex operation, one foreast-to-west transmission and one for west-to-east transmission, inorder to provide a subscribers local station with full duplex servicethrough such concentration groups, it is necessary to provide twoseparatey loop circuits extending from any subscribers premises to thetelegraph service board. One such loop connects a local station circuitincluding a telegraph transmitting and receiving instrument at thesubscribers premises with an individual in verse neutral loop repeaterat the service board terminal. It is extended via. the leg of the looprepeater into an individual concentration jack circuit. From this loopconcentration jack circuit it is connected into one of the two hubs.

In a similar manner a second sending and receiving instrument on thesubscribers premises isA connected through a loop circuit to anindividual inverse neutral loop repeater. It is extended via the leg ofthe loop repeater into an This exemplifies a typical arrangementindividual concentration jack circuit. From the concentration jackcircuit it connects to the other of the two hubs.

Thus, there is an individual hub and concentration group fortransmitting in each direction. Both are independent.

In the case of iull duplex operation,V the concentration group for theeast-to-.west hub and the concentration group ior the west-to-east hubare located at the same attendants position at the telegraph serviceboard. If it is desired, a multiple appearancey of the concentrationjacks may be provided at a second attendants position. The leg multiplejacks of the line circuits and the idle indicator lamps and controlcircuit are arranged in the saine manner as described above for a halfduplex concentration group.

Refer now to Figs. l, 6, '7 and 4 arranged for full duplex operation. Inthe numbering of the apparatus for a ull duplex concentration group,numbers only, without any letter suixes, will be usedl as both stationloops extend to thev station of but one patron and the sending leg ofone line repeater is connected to the receiving leg of its cooperatingline repeater.

It was shown in the description above that the east line in Fig. 1 wasconvertible from a full duplex to a half duplex and vice Versa. It wasshownv that when a line was released froma concentration group orserving as a spare: line, the relay such as i i3' in the line repeaterwas released and the line repeater was conditioned to function as a fullduplex repeater. In such` case two separate legs extended fromv therepeater through the leg multiple circuit. On the other hand, when aline was normally connected to a half duplex concentration group, relayl I3 was operated and only one leg from the line repeater was used,k inwhich case sendingl and receiving was performed over the single leg. Inthe arrangement now to be described, the line is normally connected intoa full duplex concentration group. Under such a condition relay H3vremains released and two legs extend from the line repeater through theleg multiple circuit and into separate line concentration jacks for eachleg. To. provide for the four line legs from the two lines, four sets ofline concentration jacks are required. When signals are transmitted fromthe distant terminal to the east, negative battery and ground, arealternately connected to receive leg conductor |20. Conductor i20-connects through conductors 62?] and 120, through thef top outerarmature and backV contact. of relay 1.0i, through test resistance 192,and the back contact and armature of relay m3 to hub 16,4 which is theeast-to-west hub.

Thek send leg, by meansv of which signals are transmitted to the distantwest terminal, is connected to the same hub, so that the east termi,-nal may transmit to the west terminal. The circuit may be traced fromhub 'm4, through the ar- 'mature and back contact of relay 133',resistance T06, throughthetop inner back contact-and armature o relay i,through` conductors 136; S36 and |36 into the rectangle exemplifyingtherwest repeater and line. There theV path will be continuedl throughthe left-hand breakv contact and armature of a relay such as ll'3 (whichremains released), through the bottom windings of relays such as H9 andi i8 in series, through resistances such as H1 and H6 in series tonegative battery such as H5. Thus signals impressed on relays lill' andm2 at the east terminal` passi through hub lill! to a receiving relaysuch as |21 at the west terminal.

In a similar manner, signals impressed on relays vsuch as l iii and |82at the west terminal connect negative battery and ground for marking andspacing through the contacts of a relay such as I |2 in the westrepeater. These signals are impressed through conductors ISI, 63| and13|, through the top outer armature and back contact of relay 181,through resistance 108 to hub 135, which is the west-to-east hub. Fromhub 185 a path may be traced through the armature and back contact ofrelay 'm9, resistance 1li), top inner back contact and armature of relayconductors 132, 632 and I 32, left-hand back contact and armature ofrelay H3, bottom windings of relays ||9 and H8, resistances ||1 and H6to negative battery l5. This results, as has been previously shown, inthe reception of signals by receiving relay |21 at the east terminal.vOne loop from the local station is connected through an individual looprepeater and an individual group of concentration jacks to hub 104, andthe other through corresponding facilities to hub 155.

yIn tliestation circuit shown in Fig. 6 there is a telegraph key and asounder in each loop. The equipment in the station loops may be variedto suit conditions. For example, where a station circuit is to berestricted to receiving only, the equipment on the loop would compriseonly a sounder. The polar relay, by means of which 'the inverse neutralrepeater receives signals transmitted from the local station andtransmits them toward the hub, would be blocked in the mark position orwould be removed from its jack mounting and replaced with a dummy relaybase strapped to obtain the same eiect. Such loops would not be equippedfor calling in the service board attendant, hence the call signal key,at the station, corresponding to key 221 in Fig. 2 and thedifferentially connected relay, such as 286 in Fig. 2, would be omitted.

AWith the concentration group described, the east and west line maycommunicate on a full duplex basis. Signals transmitted from the easttothewest terminal will be recorded by the sounder in-'one loop at thelocal station. Signals transmitted from the west to the east terminalwill be recorded'by the receiving instrument in the other loop at thelocal station. The telegraph key in one loop at the local station may beused to communicate with the east terminal. .The ltransmitter in theother loop at the local station may be used to communicate with the westterminal.

Attention was called above to the fact that the connections for fullduplex service are widely Variable dependent on` the traliric desired.As an illustration, it is possible to connect a group of lines such asdescribed herein, so that they radiate from a service board in manydirections and to interconnect all of their sending legs intoacommonhub. A loop from a local station having a transmitting instrument couldbe connected to the common hub to establish a broadcast arrangement. Allof the receiving legs of line repeaters from the various distantterminals could be connected into a common hub and extended through aseparate loop to the receiving instrument at the local station.Transmission from the various distant stations to the local stationcould'be scheduled on a time basis to prevent interference or, if onedistant terminal were transmitting to the local station and a secondReleasing a Zine from a full duplex concentration group The manner inwhich a line which normally forms part of a full duplex concentrationgroup is released from a concentration group will now be described.

To exemplify this operation the east line will be released from theconcentration group described above. To release the east line, a ringsleeve short circuiting plug, such as plug 3|2, is inserted in jack A1|This establishes a circuit from ground, throu-gh the sleeve of jack 1H,sleeve of plug 3|2, ring of plug 3|2, ring of jack 1|| and top windingof relay 1|2 to battery, operating relay 1|2. The operation of relay 1|2in turn operates relay 10| over` an obvious circuit, to break theconnections of the send and receive legs of the east line from hubs and1M at the top inner armature and back contact and top outer armature andback contact, respectively, of relay 1|] The west line may be releasedby a similar operation performed in a corresponding jack in the westline.

Replacing a line forming pant of a full duplex concentration group witha line which has been released from a different concentratiOn group Inorder to substitute a released line for a line normally forming part ofa full duplex concentration group, it is first necessary to nd areleased idle line Vto the desired distant terminal which is availableto serve as a substitute. In the case of all idle lines, both releasedand spare, a path is closed from ground connected to the filaments 'ofthe idle indicating lamps of each circuit in multiple, through itsassociated leg multiple circuit, to battery in the idle indicatorcontrol circuit. The attendant operates the idle indicator control keyat the position Where the concentration group is being administered.This lights the multiple lamps of every telegraph line in the serviceboard which is not at the moment serving in a concentration group. Theattendyan1;4 selects one connected to the desired distant terminal fromreference to a designation strip associated with the lighted lamps. Apatch is made from the multiple jack associated with the available line,at the attendants position Where the concentration group is administeredto the control jack of the line in the full duplex concentration groupwhich is to be released and replaced bythe newline. vThis automaticallyreleases the old line; and connects the two legs of the new line intothe'tWo hubs.

It will be assumed, in order to demonstrate this operation, that theconcentration group con- Vsists of the west line and the local stationloops. It will be assumed also that the east line is idle. The' eastVline, it will be assumed, normally forms part of another concentrationgroup instead of the concentration group described above, from whichother concentration group it has been released by an operation such asdescribed in the preceding section herein.

Under the above circumstances, the two line concentration jack circuitsassociated with the two 'legs of theveast line would appear at theposition where rthe concentration group with vvhichthe east line isnormally associated is ad-

